In recent years, organic EL (Electro-Luminescence) elements used for lighting devices have gained attention.
When such organic EL elements are used for products in the field of lighting (hereinafter referred to as organic EL lighting devices), a problem in which shortcircuits occur between their anode and cathode arises as a vitally important issue.
Since organic EL lighting devices have a large light emission area to which an electric field is applied, the likelihood of an occurrence of shortcircuits in the devices may become high and thereby the yield and reliability may deteriorate.
The reasons why shortcircuits occur are, for example, a surface gap that is present on a transparent conductive film (ITO) that is a base layer of an organic layer and that is used for an anode and foreign matter such as dust that adheres between the anode and cathode. Since they may damage an organic film on the ITO or decrease the film thickness, the distance between the anode and cathode may decrease. As a result, shortcircuits may occur at portions locally exposed to a high electric field.
A surface gap may occur due to ITO grains, crystalline particles, foreign matter such as dust that adheres to the ITO that is formed, sediment of Ce used for abrading SiO2 that is the base layer of the ITO, or the like.
To prevent shortcircuits from occurring in the devices, before their shipment, they might be aged and repaired.
However, to prevent shortcircuits from occurring, a technique that applies a forward bias voltage between the anode and cathode of each organic EL element, successively turns on the organic EL elements, and then locally breaks down and insulating portions in which shortcircuits occur, by using laser light, may be used.
In the ordinary aging and repairing technique, products need to be powered until shortcircuits have not occurred for a predetermined long period so as to improve their reliability. Equipment and space will be required for all products that are to be aged.
Another repairing technique that applies a forward bias voltage that is equal to or lower than the light emission voltage of an organic EL element (in which no shortcircuit occurs) to each organic EL element, weakly lights portions that are thinner than normal portions, recognizes their images, and repairs them by using laser light is also known.
A further repairing technique that applies a backward bias voltage (DC) to each organic EL element and locally repairs portions that are thinner than normal portions with a reverse current is used. However, in this technique, the applicable voltage is low and thus many portions are susceptible to the occurrence of shortcircuits. As a result, it is necessary to employ one of the foregoing two techniques.
As such a related art reference, a technique that increases a reverse bias voltage applied to each organic EL element and thereby repairs portions in which shortcircuits occur is disclosed (refer to for example Patent Literature 1).